Mycobacterial SigA and SigB Cotranscribe Essential Housekeeping Genes during Exponential Growth

All mycobacteria encode a group II sigma factor, σ B , closely related to the group I principal housekeeping sigma factor, σ A . Group II sigma factors are widely believed to play specialized roles in the general stress response and stationary-phase transition in the bacteria that encode them. Contrary to this widely accepted view, we show an additional housekeeping function of σ B that complements the function of σ A in logarithmically growing cells. These findings implicate a novel and dynamic partnership between σ A and σ B in maintaining the expression of housekeeping genes in mycobacteria and can perhaps be extended to other bacterial species that possess multiple group II sigma factors.